It is well-established that selecting a silicone polymer for textile finishing often requires a trade-off in properties. For example, softness and non-yellowing are a highly desired combination of properties for textiles such as fibers and fabrics, both woven and non-woven. By softness is meant the quality perceived by users through their tactile sense to be soft. Such tactile perceivable softness may be characterized by, but not limited to resilience, flexibility, and smoothness and subjective descriptions such as "feeling like silk or flannel."
Aminopolysiloxanes are known to impart such softness or improve the "hand" of a textile. It has been generally understood that softness of a textile treated with an aminopolysiloxane is directly related to the amine content (the number of amino-functional groups) of the polysiloxane. That is, as the amine content of the aminopolysiloxane used to treat the textile is increased, the softness imparted to the textile increases. Conversely, as the amine content of the aminopolysiloxane is decreased, likewise, the softness of the textile decreases. Unfortunately, as the amine content of the aminopolysiloxane is increased to provide softness to a textile, it also causes the textile to discolor or yellow. That is, the higher the amine content of the aminopolysiloxane used to treat a textile, the more discolored or yellowed the textile becomes.
When yellowing of the textile is a concern, it has been the textile industry's practice to impart softness to a textile by treating it with an aminopolysiloxane in which the amino-functional groups have been chemically modified so that such groups are less reactive or susceptible to oxidation, and, hence, less yellowing. Textile treatment using such chemical modification include treating a textile with a polysiloxane containing amide groups or carbamate groups to provide a soft, less-yellowed textile. However, those skilled in the art in assessing softness have reported that these polysiloxanes whose chemical reactivity have been modified by forming amide or carbamate groups do not possess or retain what has been subjectively described as "the amine-like softness or amine-like hand." That is, a textile treated with a polysiloxane modified by amide or carbamate groups does not have the same subjective feel of softness as a textile treated with an unmodified, reactive aminopolysiloxane.
Commercially, to maintain an amine-like hand or amine-like softness, textiles have been treated with aminopolysiloxanes having an amine content ranging from about 0.4 to 2.5 percent by weight as NH.sub.2. However, textiles treated with aminopolysiloxanes having this level of amine content are known to exhibit yellowing. Additionally, treating a textile with such levels of amine content or higher levels may raise environmental acceptability concerns. For example, treating textiles with an aminopolysiloxane having such level of amine content may cause corrosivity, irritation to skin and eyes, and/or breathing difficulty during application. Accordingly, there is an on-going need to provide a method for treating a textile to impart "amine-like" softness and reduced yellowing and which method is more environmentally acceptable.
The textile industry has commonly characterized aminopolysiloxanes used to impart softness and other polysiloxanes (substituted with other functional groups and unsubstituted alike) by the viscosity. In general, it has been widely believed in the textile industry that the viscosity of polysiloxanes (substituted and unsubstituted) useful in textile treatment may vary so long as the polysiloxane is flowable or can be made flowable for a particular application. The industry has used viscosity to characterize polysiloxanes useful in textile treatment stating that viscosity is directly related to molecular weight and more easily ascertainable than molecular weight when the polysiloxane formula or the raw materials from which it was made are unknown. See, for example, U.S. Pat. No. 5,059,282 at Col. 2, lines 46-68 and Col. 8, lines 3-30, and Silicon Compounds, 1987, pp. 262 distributed by Petrarch Systems (Bristol, Pa.). However, for a substituted polysiloxane such as an organomodified polysiloxane, for example, an aminopolysiloxane, a direct correlation between viscosity and molecular weight is more complex. For a given degree of polymerization, the viscosity of organomodified polysiloxanes is related to the type of organo-functionality (i.e., amino, carboxyl, carbonyl) and to the amount of that functionality in the polymer. As a consequence of the wide use of viscosity to characterize various polysiloxanes, especially aminopolysiloxanes, the importance of the combination of the amine content and molecular weight on the aminopolysiloxane's ability to provide softness, especially softness with non-yellowing has not been recognized.